Noise Abatement System Research Articles

Sonic crystal green walls based on a combination of cylinder scatterers and vegetation for noise mitigation in urban design

This study proposes sonic crystal green walls based on combined cylinder scatterers and vegetation. It has been known that the vegetation or greenery system is effective in dealing with environmental pollutants, while the cylinder scatterer arranged periodically, also known as a sonic crystal, is preferable owing to the capability of noise attenuation, light transmission, and air circulation simultaneously. Combining both components into a single noise abatement system is expected to provide acoustical and non-acoustical features for urban design, where such an approach maximizes the merit of each component. Moreover, the system is useful for advocating sustainability amid global warming issues. In this work, a numerical model is developed using finite element method (FEM), while experimental results are provided to validate the absorption and attenuation results. It is found that the sonic crystal can attain an attenuation of 13.5 dB around 1.6 kHz. Such a promising result is extended further to lower frequency under a specific configuration of scatterers corresponding to lattice distance and filling faction ratio parameters. Meanwhile, the vegetation can enhance overall attenuation at higher frequencies.

The Aerodynamic Characteristics Investigation on NACA 0012 Airfoil with Owl’s Wing Serrations for Future Air Vehicle

Owls have an incredibly unique ability to fly in silence, and this ability has significant potential to reduce noise pollution from aircraft engines. For decades, researchers have been studying the noise abatement system in conventional aircraft, but only a few of them had looked into the owl’s ability to reduce the aircraft noise level, especially on the serrated wing. The present study aims to investigate the lift and drag coefficient of the serrated wings including leading-edge serrations, trailing-edge serrations, both-edge serrations, and the original/baseline wing model from the NACA 0012 airfoil. The experimental testing was performed in a wind tunnel at Reynolds numbers of 20,000 and 40,000 and angle of attack from 2° to 30°, in 2° angle intervals. In general, the results showed that each wing model produced a similar lift and drag coefficient profiles, which were proportional to the angle of attack. At Reynolds number of 40,000, the lift coefficient increases from 0.45 to 1.5, as the angle of attack increases from 2° to 24°. Afterward, it decreased as the angle of attack exceeded 24°. According to the data, the trailing-edge serrations model showed the lowest drag coefficient at a Reynolds number of 40,000. Meanwhile, the highest lift coefficient at Reynolds number of 40,000 had been produced by the baseline wing model. This result is beneficial in reducing the noise generation produced by wing structure and at the same time enhancing aerodynamic efficiency.

Noise reduction of pile driving and unexploded ordinance detonations at offshore wind farm installation sites

Pile driving noise during the installation of monopile foundations for offshore wind farms can produce very high noise levels, and strict regulations on this underwater noise exist around the world. In addition, the controlled detonation of unexploded ordinance (UXO) at offshore wind farm installation sites in European waters is an additional challenge and reduction of this noise is a major challenge. This paper discusses a tunable acoustic resonance-based underwater noise abatement system for use on marine pile driving, controlled UXO detonations, and other applications. The system consists of arrays of underwater air-filled resonators, which surround the noise source and are tuned to optimally attenuate noise in a frequency band of interest. System demonstrations that were conducted at two offshore wind farm sites in the North Sea will be discussed, in which peak sound pressure level reduction of nearly 40 dB was measured, and almost 20 dB sound exposure level reduction was measured. Laboratory testing on noise generated by a combustive sound source, used to simulate UXO noise, will also be discussed. The method of deploying these resonator arrays in a simple collapsible framework, operational advantages of this approach, and future projects using this technology will be shared.

Examples of both expected and unexpected interactions and outcomes when conveying science and technology to traditional print and modern media journalists

It has been my experience with both traditional print journalists, and with modern media journalists, that unexpected interactions and outcomes sometimes occur. These can have both desirable and undesired consequences for the scientist. Some examples of these interactions will be given, which are associated with quite diverse technical topics, ranging from press and radio interviews covering work on the soundscape of a threatened species (Ceratotherium simum simum, the southern white rhinoceros), to a radio interview on the acoustics of coffee roasting that included a surprise guest, to an underwater photo shoot with a National Geographic photographer covering research on an underwater noise abatement system. Some guidelines will be presented that aim to minimize the undesired outcomes.

Using arrays of air-filled resonators to attenuate low frequency underwater sound

This paper investigates the acoustic behavior of underwater air-filled resonators that could potentially be used in an underwater noise abatement system. The resonators are similar to Helmholtz resonators without a neck, consisting of underwater inverted air-filled cavities with combinations of rigid and elastic wall members, and they are intended to be fastened to a framework to form a stationary array surrounding a noise source, such as a marine pile driving operation, a natural resource production platform, or an air gun array, or to protect a receiving area from outside noise. Previous work has demonstrated the potential of surrounding low frequency sound sources with arrays of large stationary encapsulated bubbles that can be designed to attenuate sound levels over any desired frequency band and with levels of reduction up to 50 dB [Lee and Wilson, Proceedings of Meeting on Acoustics 19, 075048 (2013)]. Open water measurements of underwater sound attenuation using resonators were obtained during a set of lake experiments, where a low-frequency electromechanical sound source was surrounded by different arrays of resonators. The results indicate that air-filled resonators are a potential alternative to using encapsulated bubbles for low frequency underwater noise mitigation. [Work supported by AdBm Technologies.]

Acoustic measurements and modeling of air-filled, underwater resonator cavities

This paper investigates the near-resonance acoustical properties of submerged air-filled resonators intended for use in an underwater noise abatement system. These resonators are a potential alternative to encapsulated bubbles. The resonators are similar to Helmholtz resonators in shape and design, but without a neck, consisting of underwater inverted air-filled cavities with rigid walls. A finite element model was developed to investigate the acoustic behavior of the resonators near their resonance frequencies, and based on the results of the model, physical realizations of the resonators were designed and fabricated for testing. Experiments were performed with the resonators in a closed water-filled tank operated in the long wavelength limit [J. Acoust. Soc. Am. 132, 2039 (2012)], where their resonance frequencies and Q-factors were measured using the technique described by Leighton et al., [J. Acoust. Soc. Am. 112, 1366–1376 (2002)]. Comparison between the results from the measurements and modeling will be discussed. [Work supported by Shell Global Solutions.]

Attenuation of sound in water through collections of very large bubbles with elastic shells

The ultimate goal of this work is to accurately predict the attenuation through a collection of large (on the order of 10 cm radius) tethered encapsulated bubbles used in an underwater noise abatement system. Measurements of underwater sound attenuation were performed during a set of lake experiments, where a low-frequency compact electromechanical sound source was surrounded by different arrays of encapsulated bubbles with various individual bubbles sizes and void fractions. The measurements are compared with an existing predictive model [J. Acoust. Soc. Am. 97, 1510–1521 (1995)] of the dispersion relation for linear propagation in liquid containing encapsulated bubbles. Although the model was originally intended to describe ultrasound contrast agents, it is evaluated here for large bubbles, and hence low frequencies, as a design tool for the underwater noise abatement system, and there is fairly good quantitative agreement between the data and the model. Refinements to the model to incorporate multiple scattering effects, which may be important at high void fractions, via an effective medium approach [J. Acoust. Soc. Am. 111, 168–173 (2002)] and comparison with the data will also be discussed. [Work supported by Shell Global Solutions.]

Measurements of resonance frequencies and damping of large encapsulated bubbles in a closed, water-filled tank

The ultimate goal of this work is to accurately predict the resonance frequencies of large (on the order of 10 cm radius) tethered encapsulated bubbles used in an underwater noise abatement system, and also to investigate ways to enhance the system’s efficacy over the use of air-filled bubbles alone. Toward that end, a closed water-filled tank was developed for the purpose of measuring the resonance frequency and damping of single large tethered encapsulated bubbles. The tank was designed to be operated in the long wavelength limit for frequencies below the lowest tank resonance, which was chosen to be 500 Hz, using the method described be Leighton, et al. [J. Acoust. Soc. Am. 112, 1366--1376 (2002)]. Individual bubble resonance frequencies and Q-factors were measured for encapsulated bubbles of various sizes. The effects of the encapsulating material and wall thickness were investigated, along with the effects of alternative fill gases and internal heat transfer materials. Experimental results are compared with an existing predictive model [J. Acoust. Soc. Am. 97, 1510--1521 (1995)] of bubble resonance and damping. [Work supported by Shell Global Solutions.]

Scattering by a cylinder covered with an arbitrary distribution of impedance and application to the optimization of a tramway noise abatement system

A semi-analytical solution for the two-dimensional scattering of a line source by a cylinder with an arbitrary distribution of surface impedance and its image with respect to a vertical baffle is derived. This description is used to model the shadowing due to a low-height semi-cylindrical noise barrier close to a tramway. After validation against the boundary element method, this solution is used in a gradient-based optimization approach of the admittance distribution to maximize the broadband insertion loss in a given receiver zone. First, a hypothetical but passive distribution is found, showing an improvement of more than 20dB(A) with respect to a purely rigid barrier. Second, a feasible optimized surface treatment made of a porous layer and a micro-perforated resonant panel is proposed, with an improvement of 14dB(A) with respect to an entirely rigid barrier and 8dB(A) with respect to a uniform absorbent barrier. The optimization provides an automatic way of tuning the resonant panel so that the attenuation is enhanced in the frequency band where the source has the most spectral content. The benefit of using a non-uniform admittance distribution is evaluated in this idealized context to be about 8dB(A).

A comparative study on energy consumption for HVAC systems of high-tech FABs

The unique system dynamics of five different HVAC designs including the RCU (recirculation air unit) system, the MAU (make-up air unit) + RCU system, the MAU + RCU + FCU (fan coil unit) system, the MAU + axial fan system, and the MAU + FFU (fan-filter unit) system for a typical 200 mm DRAM wafer fabrication plant are discussed and compared. The energy performances of the RCU system, the MAU + RCU system, the MAU + RCU + FCU system, and the MAU + axial fan system are 3.8, 1.19, 1.12 and 1.08, respectively, folds that of the most efficient MAU + FFU system. The MAU + axial fan system exhibits slight less efficient in energy performance, compared with the MAU + FFU system. The most influential factor on energy performance between these two systems is the design of the noise abatement system, especially the pressure drop of the silencer, which dominates almost half of the internal static pressure of axial fan. When the static pressure of silencer of the MAU + axial fan system is reduced to 50 Pa, energy consumption of these two systems is comparable. Bypassing a certain portion of FAB return air to mix with make-up air can maximally reduce 50% of energy consumption of the RCU system.

Modular leads frame with noise abatement system and pile feeder

A modular leads frame for a pile driving machine is provided with a plurality of noise abating shield members which surround the driving hammer of the pile driving machine with certain ones thereof being moved with the driving hammer throughout its driving stroke in order to abate the noise resulting from the driving impact of the hammer against the pile. The pile is fed into position by first hoisting the movable shield members and the driving hammer to the top of the leads frame, hoisting the pile to be driven into a vertical position after attaching the pile hoist line to one end of the pile at ground level and thereafter actuating a pile feeder which positions the vertically hoisted pile within the leads frame and in alignment with the driving hammer.

The development of noise abatement configurations adaptable to amphibious life science studies scheduled for Spacelab projects

Due to the adverse intensity of the acoustic noise within Spacelab, which will be generated during the launch of Space Shuttle, it has been determined that mitigating measures must be implemented in order to preserve the integrity of certain data to be collected during in‐orbit amphibious life sciences experiments. Because of dynamic experimentation constraints, the preliminary design of the noise abatement system required the utilization of performance trade‐offs resulting in the development of a multicomponent system to achieve effective noise control capabilities. A double‐walled life support container fully filled with water and a specimen cadaver has been experimentally modelled in full scale. Its design is intended to merge noise control capabilities with life support, data acquisition, and dynamic requirements in order to achieve the significant noise reduction required by the project.